• Journal of Mechanical Science and Technology
• /
• 제14권7호
• /
• pp.789-795
• /
• 2000

Free-surface flows with an arbitrary deformation, induced by a submerged hydrofoil, are simulated numerically, considering two-fluid flows of both water and air. The computation is performed by a finite volume method using unstructured meshes and an interface capturing scheme to determine the shape of the free surface. The method uses control volumes with an arbitrary number of faces and allows cell wise local mesh refinement. The integration in space is of second order, based on midpoint rule integration and linear interpolation. The method is fully implicit and uses quadratic interpolation in time through three time levels. The linear equations are solved by conjugate gradient type solvers, and the non-linearity of equations is accounted for through Picard iterations. The solution method is of pressure-correction type and solves sequentially the linearized momentum equations, the continuity equation, the conservation equation of one species, and the equations for two turbulence quantities. Finally, a comparison is quantitatively made at the same speed between the computation and experiment in which the grid sensitivity is numerically checked.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2002년도 추계학술대회 논문집
• /
• pp.375-378
• /
• 2002

In this paper, the frequency response separation scheme is proposed for high scanning speed and simple structure of non-contact type of AFM. A self-sensing cantilever is attached on the actuator for detect the atomic force between tip and the media surface. VCM or PZT are used for actuator. This paper presents the method to simplify the actuator structure and the performance of each actuator for non-contact type AFM. Based on the frequency response separation scheme, the only one actuator plays roles 1311owing low frequency surface and modulating self-sensing cantilever tip in contrast with convention non-contact type AFM. 10 ${\mu}{\textrm}{m}$ standard grid sample imaged to verify proposed scheme. This result shows the possibility simplifying the actuator structure and reducing cost of non-contact type AFM.

• Journal of Korean Society for Atmospheric Environment
• /
• 제15권E호
• /
• pp.45-54
• /
• 1999

The effectiveness of NOx emission reductions from power plants to alleviate persistent ozone nonattainment in the esterm Unites States was investigated with a focus on the Northeast Corridor, centered on New York City. The 1995 ozone episode along with the 2007 base case emission scenario was used with the Variable-Grid Urban Airshed Model(UAM-V) to determine ozone concentrations. Several scenarios based on EPA's proposal issued on October 10, 1997 were examined. Although it is widely recognized that the eastern United States includes a large Nox-sensitive region(e.g., Sillman, 1999), the study revealed that reducing NOx emissions from power plants beyond 500 miles (800km) was not effective for reducing ozone exceedances in the region. It was also found that NOx emissions from power plants play an important role in local ozone exceedances.

• 조명전기설비학회논문지
• /
• 제28권12호
• /
• pp.65-73
• /
• 2014

In this paper, the detection scheme of the voltage variation using a two difference voltage is proposed. The conventional sag detector is from a single-phase digital phase-locked loop (DPLL) that is based on a d-q transformation using an all-pass filter (APF). The APF generates a virtual q-axis voltage component with $90^{\circ}$ phase delay but the APF cannot generate the virtual q-axis voltage depending on the phase of the grid voltage. To overcome the problem, q-axis voltage component is generated from difference between the current and previous value of d-axis voltage component in the stationary reference frame. However, the difference voltage around the zero crossing is not enough to detect the voltage sag. Therefore, the new detection scheme using the two difference voltage which can detect the sag around the zero crossing voltage is proposed.

• Journal of Power Electronics
• /
• 제14권5호
• /
• pp.926-936
• /
• 2014

A simplified and effective space vector pulse-width modulation (SVPWM) algorithm with two and three levels for three-phase voltage-source converters is proposed in this study. The proposed SVPWM algorithm only uses several linear calculations on three-phase modulated voltages without any complicated trigonometric calculations adopted by conventional SVPWM. This simplified SVPWM also avoids choosing the vector sector required by conventional SVPWM. A two-level overmodulation scheme is integrated into the proposed two-level SVPMW to generate the output voltage that increases from a linear region to a six-step state with a smoothly linear transition characteristic and a simple overmodulation process without a lookup table and complicated nonlinear functions. The three-level SVPWM with a proportional-integral controller effectively balances the neutral point potential of the neutral point clamped converter. Results from the simulation in MATLAB/Simulink and the experiment based on a digital signal processor are provided to clearly demonstrate the validity and effectiveness of the proposed strategies.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2017년도 전력전자학술대회
• /
• pp.437-438
• /
• 2017

본 연구는 독립 운전 모드의 P+MR 기반의 전압제어기의 계통 동기화 방식을 조사한다. 계통 복전 후 계통과의 재연결을 위한 계통 동기화가 고정자 좌표계하에서 제어가 수행되는 경우, 독립운전하에서 정전압, 정주파수를 가지는 교류 지령 전압은 계통 전압으로 대체되는데 이 부분에서 고정자 좌표계 제어하의 현재 출력 전압과 계통 전압의 위상 차이에 기인하여 상당한 전압 오차가 발생할 여지가 있고 이러한 전압 오차 발생은 심각한 전압 과도 상태를 야기할 수 있게 된다. 추가적으로, 인버터의 출력 단에 연결된 부하가 비선형 부하라면 부하에서 생성되는 고조파에 기인하여 위에 언급된 전압 과도 상태가 더욱 심각해질 수 있다. 본 논문에서는 위에 언급된 문제를 해결하기 위한 대책으로 독립 운전 모드하에서의 전압 제어를 위해 사용되는 P+MR 제어 기반의 비선형 부하를 고려한 매끄러운 계통 동기화 방식이 제안되었다. 제안된 매끄러운 계통 동기화 방식은 실험 결과를 통해 검증된다.

• 한국정보과학회:학술대회논문집
• /
• 한국정보과학회 2003년도 봄 학술발표논문집 Vol.30 No.1 (A)
• /
• pp.94-96
• /
• 2003

차세대 통신에서는 컴퓨터자원들이 지속적으로 대용량화 고속화되는 추세이며 특히 생명공학, 유전공학, 유체역학 기상기후 예측 동 여러 과학 분야에서 단일자원으로는 제공하기 힘든 계산 및 저장자원을 요구 하고 있다. 이러한 문제를 해결하기 위해서 지리적으로 분산 되어있는 자원들을 연결하여 마치 단일 차원을 사용하는 것처럼 해주는 서비스인 그리드가 대두 되었다. 그러나 그리드 사용자가 작업을 수행시키기 위해서는 자신의 DN(Distinguished Mame)을 Remote Machine상에 Local User Account를 바인딩 시켜줘야 한다. 따라서 각 사이트 관리자는 그리드 서비스를 제공하기 위해 수많은 그리드 사용자의 DN과 Local User Account를 바인딩 처리를 해 주어야 한다. 그러나 사실상 현실적으로 불가능하다. 이러한 문제를 해결하기 위해서 본 논문에서는 그리드 사용자에 대한 정책기반 접근 제어 시스템을 설계 및 구현했다.

• 한국정보처리학회:학술대회논문집
• /
• 한국정보처리학회 2014년도 추계학술발표대회
• /
• pp.707-710
• /
• 2014

최근 지능형 전력망을 통한 전기요금의 실시간 측정이 가능해지면서 시간별 전력 사용량 및 이에 해당하는 비용 산출이 가능하게 되었다. 이에 따라 전기 요금 절감을 위해서는 매 시간 전력 소모를 체크하고 제한 전력 이상을 사용하지 않아야 한다. 본 논문은 지능형 전력망 사용 빌딩에 유전알고리즘을 이용하여 전력을 효율적으로 제어할 수 있는 알고리즘을 제안한다. 각 시간대별 전력 소모량을 계산하여 제한 전력을 넘는 사용량은 다른 시간대로 분산하고 사용하지 못한 전력은 나머지 연산을 통하여 전력 소모량이 최소인 시간대에 분포시키는 나머지 연산을 적용하였다. 또한 실제 전기 사용량 데이터를 기반으로 제안기법이 시간대별 전력소모량의 편차를 해소하고, 기존 전력 사용 패턴에 비해 전력요금의 절감에 기여할 수 있음을 확인 하였다.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2012년도 전력전자학술대회 논문집
• /
• pp.134-135
• /
• 2012

This paper analyzes the characteristics of the power system of Jeju island in 2014, which has wind farms with the support of BESSs (Battery Energy Storage Systems). In the simulation, the electrical loads are predicted based on Korea Power Exchange's data and the wind turbines are considered with new installed plans within 2014. The situation that some wind farms are forced to disconnect from the grid instantaneously is considered. The BESSs are controlled by using SOC (State of Charge) and power smoothing control algorithm. The simulation results show the effectiveness of the proposed method.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2005년도 추계학술대회논문집
• /
• pp.143-146
• /
• 2005

In modern automotive control modules, mechanical failures of surface mounted electronic components such as microprocessors, crystals, capacitors, transformers, inductors, and ball grid array packages, etc., are mai or roadblocks to design cycle time and product reliability. This paper presents a general methodology of failure analysis and fatigue prediction of these electronic components under automotive vibration environments. Mechanical performance of these packages is studied through finite element modeling approach fur given vibration environments in automotive application. Using the results of vibration simulation, fatigue lift is predicted based on cumulative damage analysis and material durability information. Detailed model of solder/lead joints is built to correlate the system level model and obtain solder strains/stresses. The primary focus in this paper is on surface-mount interconnect fatigue failures and the critical component selected for this analysis is 80 pin plastic leaded microprocessor.